1. Field of the Invention
The present invention relates to a pressure-sensitive adhesive composition having antistatic property, and pressure-sensitive adhesive sheets and a surface protecting film obtained by formulating into a form of a sheet or a tape using the composition.
2. Description of the Related Art
Pressure-sensitive sheets comprising an antistatic pressure-sensitive adhesive composition of the present invention is suitably used in plastic products on which static electricity is easily generated. Inter alia, particularly, the sheets are useful as antistatic pressure-sensitive adhesive sheets used in utilities disliking static electricity such as an electronic instrument, as well as a surface protecting film used for the purpose of protecting a surface of an optical member such as polarizing plate, a wavelength plate, an optical compensating film, and a reflecting sheet.
Also, the present invention relates to a pressure-sensitive adhesive-type optical member in which an antistatic pressure-sensitive adhesive layer is disposed on an optical member. The present invention is suitably used in a pressure-sensitive adhesive-type optical member using a plastic material on which static electricity is easily generated. Inter alia, particularly, the present invention is useful as a pressure-sensitive adhesive-type optical member used in a liquid crystal display and a touch panel.
3. Background of Technique
A pressure-sensitive adhesive tape can be adhered by applying a slight pressure at a normal temperature for a short time, and is used in various utilities for connecting various articles. In addition, since a pressure-sensitive adhesive tape has an aggregating force and elasticity, the tape is suitably adhered and, conversely, can be peeled from a hard smooth surface, and is also utilized as a surface protecting film.
A surface protecting film is generally used for the purpose of preventing a flaw or a stain produced at procession or conveyance of a subject to be protected by applying to a subject to be protected via a pressure-sensitive adhesive layer coated on a protecting film side. For example, for the purpose of preventing a flaw or a stain, a protecting film is applied to an optical member such as a polarizing plate and a wavelength plate used in a panel of a liquid crystal display via a pressure-sensitive adhesive layer.
In addition, a liquid crystal display and a touch panel are used by laminating various optical films such as a polarizing plate and a wavelength plate via a pressure-sensitive adhesive layer for controlling or adjusting a vibration direction or a phase difference of light.
In these optical films, products are distributed in a form in which a separator is applied for the purpose of protecting a pressure-sensitive adhesive surface for preventing a flaw or a stain, or a surface protecting film is applied for the purpose of preventing a flaw or a stain produced at a procession or conveyance process. In addition, in a step of applying an optical film, since a separator and a surface protecting film used for the purpose of protecting these optical films become unnecessary, they are peeled and removed from an optical film.
Since the aforementioned optical film, pressure-sensitive adhesive, separator and surface protecting film are constructed of a plastic material, they have high electrical insulating property and generate static electricity upon friction or peeling. Therefore, also when a separated is peeled from a surface protecting film, static electricity is generated. In addition, static electricity is a great problem in a step of manufacturing a liquid crystal display or a touch panel. Due to this static electricity, there arises a problem that a dust is attached to a surface protecting film or an optical member, and this pollutes an optical member. A disadvantage such as occurrence of electrostatic breakage at a surrounding circuit element occurs, producing abnormal display due to disturbance of a liquid crystal orientation. Then, in order to prevent such the disadvantage, a surface protecting film is subjected to various antistatic treatments.
Previously, as an attempt to suppress the aforementioned electrification of static electricity, for example, a method of preventing electrification by adding a low-molecular surfactant to a pressure-sensitive adhesive, and transferring a surfactant from a pressure-sensitive adhesive to an adherend has been disclosed (for example, see Patent Publication 1). However, the low-molecular surfactant is easily bled on a surface of a pressure-sensitive adhesive agent and, when applied to a protecting film, staining of an adherend is feared. Therefore, when a pressure-sensitive adhesive with a low-molecular surfactant added thereto is applied to a protecting film for an optical member, there is a problem that optical property of an optical member is deteriorated.
In addition, a method of adding an antistatic agent comprising polyether polyol and alkali metal salt to an acryl pressure-sensitive adhesive to suppress an antistatic agent from bleeding on a surface of a pressure-sensitive adhesive has been disclosed (for example, see Patent Publication 2). However, also in this method, bleeding of an antistatic agent is not avoided, and it has been found out that, when applied to a surface protecting film, staining of an adherend occurs with time or under a high temperature.
In addition, a surface protecting film in which an antistatic layer is disposed on one side of a plastic film has been disclosed (for example, see Patent Publication 3). However, in this surface protecting film, since electrification preventing treatment is performed on a support side, electrification prevention of a surface protecting film side can be performed, but electrification prevention of a subject to be protected can not be performed, and there is a problem that, when a surface protecting film is peeled from a subject to be protected, a subject to be protected is electrified.
For example, a method of performing electrification preventing treatment by forming an electrically conductive layer of indium oxide-tin oxide on a polarizing plate by sputtering has been disclosed (for example, see Patent Publication 4). In addition, a method of forming an electrification preventing layer comprising a ultraviolet-ray curing-type acryl resin blended with a metal oxide particle on a polarizing plate has been disclosed (for example, see Patent Publication 4).
However, in these procedures, a step for forming an electrification preventing layer on an optical member becomes necessary newly, productivity is reduced due to increase in a step, and a cost is increased. Therefore, a polarizing plate on which an electrification preventing layer is provided has a problem of a higher cost as compared with the previous polarizing plate which is not electrification prevention-treated.
On the other hand, a polarizing member on which a light diffusion layer having electrification preventing ability is formed by adding an antistatic agent to a light diffusion layer is known (for example, see Patent Publication 6), but this light diffusion layer is used for diffusing light from back light, and is not generally used in an optical member.
[Patent Publication 1] JP-A No. 9-165460
[Patent Publication 2] JP-A No. 6-128539
[Patent Publication 3] JP-A No. 11-256116
[Patent Publication 4] JP-A No. 6-51121
[Patent Publication 5] JP-A No. 2001-318230
[Patent Publication 6] JP-A No. 2002-22960